Pull ScopeInfo implementation into its own file.

The infrastructure for -Warc-repeated-use-of-weak got a little too heavy
to leave sitting at the top of Sema.cpp.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164856 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed